Temperature controlled hot edge ring assembly

ABSTRACT

A temperature-controlled hot edge ring assembly adapted to surround a semiconductor substrate supported in a plasma reaction chamber is provided. A substrate support with an annular support surface surrounds a substrate support surface. A radio-frequency (RF) coupling ring overlies the annular support surface. A lower gasket is between the annular support surface and the RF coupling ring. The lower gasket is thermally and electrically conductive. A hot edge ring overlies the RF coupling ring. The substrate support is adapted to support a substrate such that an outer edge of the substrate overhangs the hot edge ring. An upper thermally conductive medium is between the hot edge ring and the RF coupling ring. The hot edge ring, RF coupling ring and annular support surface can be mechanically clamped. A heating element can be embedded in the RF coupling ring.

BACKGROUND

Plasma processing apparatuses are used to process substrates bytechniques including etching, physical vapor deposition (PVD), chemicalvapor deposition (CVD), ion implantation, and resist removal. One typeof plasma processing apparatus used in plasma processing includes areaction chamber containing top and bottom electrodes. An electric fieldis established between the electrodes to excite a process gas into theplasma state to process substrates in the reaction chamber.

SUMMARY

According to one embodiment, a temperature-controlled hot edge ringassembly adapted to surround a semiconductor substrate supported in aplasma reaction chamber includes a substrate support having an annularsupport surface surrounding a substrate support surface. Aradio-frequency (RF) coupling ring overlies the annular support surface.A lower gasket is between the annular support surface and the RFcoupling ring. The lower gasket is thermally and electricallyconductive. A hot edge ring overlies the RF coupling ring. The substratesupport is adapted to support a substrate such that an outer edge of thesubstrate overhangs the hot edge ring. An upper thermally conductivemedium is between the hot edge ring and the RF coupling ring.

According to another embodiment, a temperature-controlled hot edge ringassembly adapted to surround a semiconductor substrate support in aplasma reaction chamber includes a substrate support with an annularsupport surface surrounding a substrate support surface. Aradio-frequency (RF) coupling ring is mechanically clamped to theannular support surface and a thermally insulative medium is between theannular support surface and the RF coupling ring. A hot edge ring ismechanically clamped to the RF coupling ring and a thermally conductivemedium is between the hot edge ring and the RF coupling ring.

According to a further embodiment, a temperature-controlled hot edgering assembly adapted to surround a semiconductor substrate supported ina plasma reaction chamber includes a substrate support with an annularsupport surface surrounding a substrate support surface. Aradio-frequency (RF) coupling ring is mechanically clamped to theannular support surface and a lower thermally conductive medium isbetween the annular support surface and the RF coupling ring. A hot edgering is mechanically clamped to the RF coupling ring and an upperthermally conductive medium is between the hot edge ring and the RFcoupling ring. The substrate support is adapted to support a substratesuch that an outer edge of the substrate overhangs the hot edge ring.

BRIEF DESCRIPTION OF FIGURES

FIGS. 1A-1B illustrate a portion of an embodiment of a showerheadelectrode assembly and a substrate support for a plasma processingapparatus, including a hot edge ring assembly.

FIGS. 2A-2B show an embodiment of a hot edge ring assembly with a hotedge ring, an RF coupling ring and substrate support with an annularsupport, including lower and upper thermally conductive media.

FIGS. 3A-3C show another embodiment of a hot edge ring assembly with ahot edge ring, an RF coupling ring and substrate support, includingpressurized heat transfer gas as a thermally conductive medium.

FIGS. 4A-4C show another embodiment of a hot edge ring assembly with ahot edge ring, an RF coupling ring with a heating element, and substratesupport including pressurized heat transfer gas as a thermallyconductive medium.

FIG. 5 illustrates temperature profiles of the hot edge ring duringmultiple plasma processing cycles using different lower and upperthermally conductive media.

FIGS. 6A-6B illustrate temperature profiles of the hot edge ring as afunction of varying static pressure of a helium heat transfer gas.

FIGS. 7A-7B illustrate temperature profiles of the hot edge ring as afunction of varying static pressure of helium heat transfer gas in anannular channel.

FIG. 8 illustrates the effects of O-rings on temperature profiles of thehot edge ring.

FIGS. 9A-9C illustrate etching rate uniformity of photoresist using ahot edge ring assembly with different lower and upper thermallyconductive media.

DETAILED DESCRIPTION

The manufacturing of the integrated circuit devices includes the use ofplasma etching chambers, which are capable of etching selected layersdefined by openings in a photoresist mask. The processing chambers areconfigured to receive processing gases (i.e., etch chemistries) while aradio frequency (RF) power is applied to one or more electrodes of theprocessing chamber. The pressure inside the processing chamber is alsocontrolled for the particular process. Upon applying the desired RFpower to the electrode(s), the process gases in the chamber areactivated such that a plasma is created. The plasma is thus generated toperform the desired etching of the selected layers of the semiconductorsubstrate such as a wafer. However, one of the challenges associatedwith plasma processing of wafers include process drift due to the plasmanon-uniformities (i.e., the change of process performance over a certainamount of time).

For control of etch rate uniformity on a semiconductor substrate, suchas a wafer, in particular, for matching the etch rate at the center ofthe wafer to the rate at the wafer edge, wafer boundary conditions arepreferably designed for assuring continuity across the wafer in regardto the chemical exposure of the wafer edge, process pressure, and RFfield strength. As is known, an RF bias can be applied to a waferundergoing plasma processing by a powered electrode underlying anelectrostatic clamping electrode. However, because the RF impedance pathfrom the powered electrode through the electrostatic clamping electrodeand wafer to the plasma can be different than the RF impedance path froman outer portion of the powered electrode to the plasma, a nonuniformplasma density which results at the edge of the wafer can lead tononuniform processing of the wafer.

To alleviate such nonuniformities, a hot edge ring and a RF couplingring has been implemented fitting around the wafer. Improved plasmauniformity can be achieved by providing an RF impedance path which issimilar at the center and edge of a wafer undergoing plasma processing.The RF impedance path can be manipulated by choice of materials for theRF coupling ring. The overlying hot edge ring is a consumable part whichprotects the RF coupling ring from plasma erosion.

Materials for the edge ring can be selected to provide a more uniform RFimpedance path at the center and edge of the wafer so as to provide moreuniformity of the plasma density across the wafer. However, uponexposure to a heat source such as the RF plasma, the edge ring cannotcool adequately, which leads to a steady rise of its temperature. Thistemperature rise can lead to process drift (i.e., processnon-uniformity) in etch rate at the edge of the wafer when multiplewafers are processed in close succession. This inability to control thetemperature of the hot edge ring and RF coupling ring during plasmaprocessing can be problematic, resulting in an increase in etch rate atthe extreme wafer edge (e.g., the outer 5 to 7 mm of a 300 mm diametersilicon wafer), polymer deposition or “first wafer effects.”

First wafer effects refers to secondary heating of subsequent waferscaused indirectly by the heating of the first-processed wafer.Specifically, upon completion of processing of the first wafer, theheated processed wafer and the process chamber side walls radiate heattoward the upper electrode. The upper electrode then indirectly providesa secondary heating mechanism for subsequent wafers that are processedin the chamber. As a result, the first wafer processed by the system mayexhibit a larger than desired critical dimension (CD) variation thansubsequent wafers processed by the system since wafer temperaturevariation can affect CD during etching of high aspect ratio contactvias. Subsequently processed wafers may have different and/or less CDvariation than the first processed wafer due to stabilization oftemperature in the chamber. Accordingly, since process drift can becaused by the steady increase in the temperature of the edge ring overthe processing of multiple wafers, a hot edge ring assembly, whichallows improved cooling of the edge ring or temperature control of theedge ring before the next wafer is processed and thereby reduces etchrate drift is desirable.

FIG. 1A illustrates an exemplary embodiment of a showerhead electrodeassembly 10 for a plasma processing apparatus in which semiconductorsubstrates, e.g., silicon wafers, are processed. The showerheadelectrode assembly 10 includes a showerhead electrode including a topelectrode 12, a backing member 14 secured to the top electrode 12, and athermal control plate 16. A substrate support 18 (only a portion ofwhich is shown in FIG. 1) including a bottom electrode and anelectrostatic clamping electrode (e.g., electrostatic chuck) ispositioned beneath the top electrode 12 in the vacuum processing chamberof the plasma processing apparatus. A substrate 20 subjected to plasmaprocessing is electrostatically clamped on substrate support surface 22of the substrate support 18.

In the illustrated embodiment, the top electrode 12 of the showerheadelectrode includes an inner electrode member 24, and an optional outerelectrode member 26. The inner electrode member 24 is preferably acylindrical plate (e.g., a plate composed of silicon). The innerelectrode member 24 can have a diameter smaller than, equal to, orlarger than a wafer to be processed, e.g., up to 12 inches (300 mm) orlarger if the plate is made of silicon. In a preferred embodiment, theshowerhead electrode assembly 10 is large enough for processing largesubstrates, such as semiconductor wafers having a diameter of 300 mm orlarger. For 300 mm wafers, the top electrode 12 is at least 300 mm indiameter. However, the showerhead electrode assembly can be sized toprocess other wafer sizes or substrates having a non-circularconfiguration.

In the illustrated embodiment, the inner electrode member 24 is widerthan the substrate 20. For processing 300 mm wafers, the outer electrodemember 26 is provided to expand the diameter of the top electrode 12from about 15 inches to about 17 inches. The outer electrode member 26can be a continuous member (e.g., a continuous poly-silicon ring), or asegmented member (e.g., including 2-6 separate segments arranged in aring configuration, such as segments composed of silicon). Inembodiments of the top electrode 12 that include a multiple-segment,outer electrode member 26, the segments preferably have edges, whichoverlap each other to protect an underlying bonding material fromexposure to plasma.

The inner electrode member 24 preferably includes multiple gas passages28 extending through and in correspondence with multiple gas passages 30formed in the backing member 14 for injecting process gas into a spacebetween the top electrode 12 and the substrate support 18. Backingmember 14 includes multiple plenums 32 to distribute process gases tothe gas passages 28 and 30 in the inner electrode member 24 and backingmember 14, respectively.

Silicon is a preferred material for plasma exposed surfaces of the innerelectrode member 24 and the outer electrode member 26. High-purity,single crystal silicon minimizes contamination of substrates duringplasma processing and also wears smoothly during plasma processing,thereby minimizing particles. Alternative materials that can be used forplasma-exposed surfaces of the top electrode 12 include SiC or AlN, forexample.

In the illustrated embodiment, the backing member 14 includes a backingplate 34 and a backing ring 36, extending around the periphery ofbacking plate 34. In the embodiment, the inner electrode member 24 isco-extensive with the backing plate 34, and the outer electrode member26 is co-extensive with the surrounding backing ring 36. However, thebacking plate 34 can extend beyond the inner electrode member 24 suchthat a single backing plate can be used to support the inner electrodemember 24 and the outer electrode member 26. The inner electrode member24 and the outer electrode member 26 are preferably attached to thebacking member 14 by a bonding material and/or mechanical fasteners.

The backing plate 30 and backing ring 36 are preferably made of amaterial that is chemically compatible with process gases used forprocessing semiconductor substrates in the plasma processing chamber,and is electrically and thermally conductive. Exemplary suitablematerials that can be used to make the backing member 14 includealuminum, aluminum alloys, graphite and SiC.

The top electrode 12 can be attached to the backing plate 34 and backingring 36 with a suitable thermally and electrically conductiveelastomeric bonding material that accommodates thermal stresses, andtransfers heat and electrical energy between the top electrode 12 andthe backing plate 34 and backing ring 36. The use of elastomers forbonding together surfaces of an electrode assembly is described, forexample, in commonly-owned U.S. Pat. No. 6,073,577, which isincorporated herein by reference in its entirety.

In a capacitively coupled RF plasma chamber for processing largesubstrates such as 300 mm wafers, a secondary ground may also be used inaddition to the ground electrode. For example, substrate support 18 caninclude a bottom electrode which is supplied RF energy at one or morefrequencies and process gas can be supplied to the interior of thechamber through showerhead electrode 12 which is a grounded upperelectrode. A secondary ground, located outwardly of the bottom electrodein substrate support 18 can include an electrically grounded portionwhich extends generally in a plane containing the substrate 20 to beprocessed but separated by a hot edge ring 38. Hot edge ring 38 can beof electrically conductive or semiconductive material which becomesheated during plasma generation.

FIG. 1B is an enlarged view of the region A in FIG. 1A surrounding hotedge ring 38. For control of etch rate uniformity on substrate 20 andmatching the etch rate at the center of the substrate to the rate at thesubstrate edge, substrate boundary conditions are preferably designedfor assuring continuity across the substrate in regard to the chemicalexposure of the substrate edge, process pressure, and RF field strength.In order to minimize substrate contamination, the hot edge ring 38 ismanufactured from a material compatible to the substrate itself. In anexample, hot edge ring materials can include silicon, graphite, siliconcarbide or the like. In another example, hot edge ring materials caninclude quartz.

Hot edge ring 38 overlies RF coupling ring 40 which is placed on anannular support surface 42 surrounding substrate support surface 22, onthe outer periphery of substrate support 18. Substrate support 18 isadapted to support substrate 20, such that the substrate's outer edgeoverhangs hot edge ring 38. Substrate support 18 can be actively cooledwith a chilled liquid circulating in cooling passages located in theinterior of substrate support (not shown in FIG. 1A). The material forRF coupling ring 40 is chosen for tapering the RF field strength at theedge of the substrate 20 to enhance etch rate uniformity. For example,RF coupling ring 40 can be made of a ceramic (e.g. quartz, aluminumoxide, aluminum nitride) or a conductive material (e.g., aluminum,silicon, silicon carbide). Surrounding hot edge ring 38 is hot edge ringcover 44, which is composed of a dielectric material. Hot edge ringcover 44 overlies focus ring 46, which confines plasma in an area abovethe substrate 20 and can be composed of quartz.

Hot edge ring cover 44 overlies focus ring 46, which confines plasma inan area above the substrate 20 and hot edge ring cover 44 can becomposed of quartz. Further surrounding hot edge ring cover 44 is groundring cover 48. Hot edge ring cover 44 protects the ground extension fromattack by the plasma. For example, hot edge ring cover 44 and groundring cover 48 can be composed of quartz or yttria. Ground extension 49can be composed of aluminum.

During plasma processing of substrate 20, hot edge ring 38, RF couplingring 40 and substrate support 18 are exposed to a vacuum environment(i.e., less than 50 mTorr). As a result, a vacuum is formed at theinterface B between hot edge ring 38 and RF coupling ring 40; and at theinterface C between RF coupling ring 40 and substrate support 18. As thetemperature of the hot edge ring 38 increases during exposure to RFpower, the transfer of heat from hot edge ring 38 to RF coupling ring 40and substrate support 18 via thermal conduction is minimal, due to thepresence of a vacuum at the appropriate interfaces. Thus, a need existsfor the ability to control the temperature of hot edge ring 38 duringthe plasma processing of substrate 20.

FIG. 2A illustrates one embodiment of a temperature controlled hot edgering assembly 200. Substrate support 218 includes annular supportsurface 242 surrounding substrate support surface 222, on the outerperiphery of substrate support 218. RF coupling ring 240 overliesannular support surface 242 with a lower thermally conductive medium 250between annular support surface 242 and RF coupling ring 240. Hot edgering 238 overlies RF coupling ring 240 with an upper thermallyconductive medium 260 between hot edge ring 238 and RF coupling ring240. Substrate support 218 is adapted to support substrate 220, suchthat the outer edge of substrate 220 overhangs hot edge ring 238.

In one embodiment, lower thermally conductive medium 250 comprises alower gasket 252 and upper thermally conductive medium 260 comprises anupper gasket 262. Lower gasket 252 and upper gasket 262 are thermallyand electrically conductive gaskets. In a preferred embodiment, lowergasket 252 and upper gasket 262 are composed of a laminate of metal orpolymer materials; a silicone-based sheet (e.g., λGEL® COH-4000,available from GELTECH, Tokyo, Japan); a laminate of aluminum (or analuminum alloy) and filled silicone rubber (e.g., Q-PAD® II,manufactured by The Bergquist Company, Chanhassen, Minn.); or a laminateof polyimide material and filled silicon rubber (e.g., SIL-PAD® K-10,manufactured by The Bergquist Company, Chanhassen, Minn.); or apolyimide material (e.g., KAPTON® polyimide film, manufactured by DUPONT®).

Other exemplary materials for lower gasket 252 and upper gasket 262 caninclude a thermal filler material such as a silicone filled with boronnitride (e.g., CHO-THERM® 1671, manufactured by CHOMERICS), a graphitematerial (e.g., eGRAF® 705, manufactured by GRAFTECH), an indium foil,or a phase change material (PCM) (e.g., T-pcm HP105, manufactured byTHERMAGON).

FIG. 2B illustrates an embodiment of temperature controlled hot edgering assembly 200 in which hot edge ring 238 is mechanically clamped toRF coupling ring 240; and RF coupling ring 240 is mechanically clampedto annular support surface 242. RF coupling ring 240 can be bolted toannular support surface 242 with lower bolts 270 (e.g. 2 to 12circumferentiality spaced apart bolts). Hot edge ring 238 ismechanically clamped to RF coupling ring 240 with clamping ring 272,which includes radially extending flange 272A. Hot edge ring 238includes a peripheral recess 238A. Radially extending flange 272A isconfigured to mate with peripheral recess to secure hot edge ring 238 toRF coupling ring 272. Clamping ring 272 is bolted to RF coupling ringwith upper bolts 274 (e.g. 2 to 12 circumferentiality spaced apartbolts). To prevent damage to clamping ring 272 and hot edge ring 238during clamping, flat polyimide ring 276 (e.g., KAPTON® polyimide film)can be placed between clamping ring 272 and hot edge ring 238. Hot edgering 238 can be clamped to RF coupling ring 240 at a torque from about 1ft.-lb. to about 10 ft.-lb. Likewise, RF coupling ring 240 can beclamped to annular support surface 242 at a torque from about 1 ft.-lb.to about 10 ft.-lb.

FIG. 3A illustrates an additional embodiment a temperature controlledhot edge ring assembly 300, in which a pressurized heat transfer gas isused for upper thermally conductive medium 360. Substrate support 318includes annular support surface 342 surrounding substrate supportsurface 322, on the outer periphery of substrate support 318. RFcoupling ring 340 overlies annular support surface 342 with lower gasket352 as lower thermally conductive medium 350 between annular supportsurface 342 and RF coupling ring 340. Hot edge ring 338 overlies RFcoupling ring 340 with an upper thermally conductive medium 360 betweenhot edge ring 338 and RF coupling ring 340.

Upper thermally conductive medium 360 includes upper inner O-ring 363Aand upper outer O-ring 363B concentrically arranged. Hot edge ring 338,RF coupling ring 340, upper inner O-ring 363A and upper outer O-ring 363define an upper volume 366. Upper volume 366 is adapted to contain avolume of pressurized heat transfer gas, including helium, neon, argonor nitrogen. In one embodiment, the static pressure of helium in uppervolume 366 can be up to about 30 Torr. In a preferred embodiment,O-rings are composed of heat resistant fluoroelastomer (e.g., VITON®fluoroelastomer, manufactured by DUPONT®).

As illustrated in FIG. 3B, upper inner O-ring 363A and upper outerO-ring 363B can be seated in grooves 365 formed in RF coupling ring 340and hot edge ring 338. In another embodiment, as illustrated in FIG. 3C,upper inner O-ring 363A, upper outer O-ring 363B, grooves 365 andannular channel 364 are concentrically arranged, such that upper innerO-ring 363A and upper outer O-ring 363B surround annular channel 364.Annular channels 364 minimize the surface contact between heat transfergas exposed surface 338A of hot edge ring 338 and heat transfer gasexposed surface 340A of RF coupling ring 340, to provide more precisecontrol over thermal conductivity by adjusting the pressure of heattransfer gas in upper volume 366 (e.g., up to 30 Torr). In oneembodiment, the height of annular channel 364 can be from about 1 mil toabout 5 mils.

Although the FIG. 3A embodiment illustrates lower thermally conductivemedium 350 as a lower gasket 352; and upper thermally conductive medium360 as upper volume 366 defined by hot edge ring 338, RF coupling ring340, upper inner O-ring 363A and upper outer O-ring 363B, it isunderstood that lower thermally conductive medium 350 could also be alower volume of pressurized heat transfer gas (i.e., defined by a lowerinner O-ring, a lower outer O-ring, annular support surface 342 and RFcoupling ring 340). Likewise, and upper thermally conductive medium 360could be an upper gasket.

FIG. 3A also illustrates controller 380, temperature sensor 382, heattransfer gas source 384 and vacuum pump 386. Temperature sensor 382 isadapted to measure a temperature of hot edge ring 338 during plasmaprocessing and supply input signals to controller 380. Heat transfer gassource 384 and vacuum pump 386 are in fluid communication with uppervolume 366. Gas source 384 is operable to increase a static pressure inupper volume 366 in response to controller 380. Likewise, vacuum pump isoperable to evacuate volume 366 in response to controller 380.

During plasma processing of substrate 320 in a plasma processing chamberwith temperature controlled hot edge ring assembly 300, substrate 320 issupported on substrate support surface 322. A process gas is introducedinto the processing chamber and the process gas is energized into aplasma state. A temperature of hot edge ring 338 is measured. If thetemperature of hot edge ring 338 is below a target temperature, thepressure of heat transfer gas in upper volume 366 is decreased. Thisdecrease in heat transfer gas pressure in upper volume 366 restricts thetransfer of heat from hot edge ring 338 to RF coupling ring 340 (i.e. athermal choke), which permits the temperature of hot edge ring 338 toincrease from exposure to RF plasma. If the temperature of hot edge ring338 is above a target temperature, the pressure of heat transfer gas inupper volume 366 is increased. This increase in heat transfer gaspressure in upper volume 366 facilitates the transfer of heat from hotedge ring 338 to RF coupling ring 340 to the temperature controlledsubstrate support 318. During plasma processing of the substrate 320,the temperature of hot edge ring 338 can be continuously monitored andthe pressure of heat transfer gas in upper volume 366 can be adjustedaccordingly to maintain hot edge ring 338 at a desirable targettemperature. Plasma processing of substrate 320 can include plasmaetching of a semiconductor material, metal or dielectric material or;deposition of a conductive or dielectric material.

FIG. 4A illustrates an additional embodiment of active temperaturecontrolled hot edge ring assembly 400 including heating element 490embedded in RF coupling ring 440. Substrate support 418 includes annularsupport surface 442 surrounding substrate support surface 422, on theouter periphery of substrate support 418. RF coupling ring 440 overliesannular support surface 442 with lower thermally conductive medium 450between annular support surface 442 and RF coupling ring 440. Hot edgering 438 overlies RF coupling ring 440 with upper gasket 462 as upperthermally conductive medium 460 between hot edge ring 438 and RFcoupling ring 440.

Lower thermally conductive medium 450 includes lower inner O-ring 463Cand lower outer O-ring 463D concentrically arranged. Annular supportsurface 442, RF coupling ring 440, lower inner O-ring 463C and lowerouter O-ring 463D define lower volume 468. Lower volume 468 is adaptedto contain a volume of pressurized heat transfer gas, including helium,neon, argon or nitrogen.

As illustrated in FIG. 4B, lower inner O-ring 463C and lower outerO-ring 463D can be seated in grooves 465 formed in RF coupling ring 440.In another embodiment, as illustrated in FIG. 4C, lower inner O-ring463C, lower outer O-ring 463D, grooves 465 and annular channel 464 areconcentrically arranged, such that lower inner O-ring 463C and lowerouter O-ring 463D surround annular channel 464. Annular channel 464minimizes the surface contact between heat transfer gas exposed surface442A of annular support surface 442 and heat transfer gas exposedsurface 440A of RF coupling ring 440, to provide more precise controlover thermal conductivity by adjusting the pressure of heat transfer gasin upper volume 468 (e.g., up to 30 Torr). In one embodiment, the heightof annular channel 464 can be from about 1 mil to about 5 mils.

FIG. 4A also illustrates controller 480, temperature sensor 482, heattransfer gas source 484, vacuum pump 486 and power supply 488.Temperature sensor 482 is adapted to measure a temperature of hot edgering 438 during plasma processing and supply input signals to controller480. Heat transfer gas source 484 and vacuum pump 486 are in fluidcommunication with lower volume 468. Gas source 484 is operable toincrease a static pressure in lower volume 468 in response to controller480. Likewise, vacuum pump 486 is operable to evacuate volume 466 inresponse to controller 480. Power supply 488 is connected to heatingelement 490 and supplies power to heating element 490 in response tocontroller 480.

During plasma processing of substrate 420 in a plasma processing chamberwith active temperature controlled hot edge ring assembly 400, substrate420 is supported on substrate support surface 422. A process gas isintroduced into the processing chamber and the process gas is energizedinto a plasma state. A temperature of hot edge ring 438 is measured.

If the temperature of hot edge ring 438 is below a target temperature,RF coupling ring 440 is heated by supplying power from power supply 488to heating element 490. In one embodiment, the target temperature isfrom about 40° C. to about 200° C. Upper gasket 462 between RF couplingring 440 and hot edge ring 438 facilitates the transfer of heat from RFcoupling ring 440 to the hot edge ring 438. While power is supplied frompower supply 488 to heating element 490, the pressure of heat transfergas in lower volume 468 is decreased. This decrease in heat transfer gaspressure in lower volume 468 restricts the transfer of heat from theheating element 490 to temperature controlled substrate support 418(i.e., thermal choke).

If the temperature of hot edge ring 438 is above a target temperature,the power from power supply 488 is terminated (if heating element 490 isactive) and the pressure of heat transfer gas in lower volume 468 isincreased. This increase in heat transfer gas pressure in lower volume468 facilitates the transfer of heat from hot edge ring 438 to RFcoupling ring 440 to the temperature controlled substrate support 418.

During plasma processing of the substrate 420, the temperature of hotedge ring 438 can be continuously monitored and the pressure of heattransfer gas in lower volume 468 and power to heating element 490 can beadjusted accordingly to maintain hot edge ring 438 at a desirable targettemperature.

Example 1

A series of tests were performed to determine the effectiveness of lowerthermally conductive medium 250 and upper thermally conductive medium260 in the FIG. 2A embodiment in dissipating heat from hot edge ring 238during plasma processing.

Tests were performed in an EXELAN® FLEX™ etching system, manufactured byLam Research Corporation, located in Fremont, Calif. For each test, four300 mm silicon wafers were subjected to plasma processing for about 1minute. A gas mixture of 25 SCCM O₂/35 SCCM C₄F₈/500 SCCM Ar wasintroduced into the etch chamber at a pressure of 45 mTorr.Dual-frequency power was applied to a bottom electrode, about 1000 W ata frequency of about 2 MHz and about 1000 W at a frequency of 27 MHz (2kW of total power). The temperature of hot edge ring 238 was measuredwith an fiber optic temperature probe during plasma processing. Hot edgering 238 and RF coupling ring 240 were mechanically clamped at a torqueof about 2 in.-lb. to about 6 in.-lb. Materials for lower thermallyconductive medium 250 and upper thermally conductive medium 260 includedλGEL® COH-4000 gaskets, Q-PAD® II gaskets and KAPTON® gaskets.

FIG. 5 illustrates temperature profiles of the hot edge ring as afunction of time for four plasma processing cycles at a total power of 2kW. From FIG. 5, eight thermal conductive media were tested: (A) Q-PAD®lower gasket; KAPTON® upper gasket with a 2 in.-lb. torque; (B) Q-PAD®lower gasket; KAPTON® upper gasket with a 4 in.-lb. torque; (C) Q-PAD®lower gasket; KAPTON® upper gasket with a 6 in.-lb. torque; (D) Q-PAD®lower and upper gasket with a 2 in.-lb. torque; (E) Q-PAD® lower andupper gasket with a 4 in.-lb. torque; (F) Q-PAD® lower and upper gasketwith a 6 in.-lb. torque; (G) λGEL upper gasket; no lower thermallyconductive medium; and (H) no lower and upper thermally conductivemedia.

For each of the temperature profiles (A)-(H) in FIG. 5, each localtemperature minima represents the beginning of the next plasmaprocessing cycle. As illustrated in temperature profile (H) (no upper orlower thermally conductive media), the temperature of each local minima(indicated by the arrows in FIG. 5) progressively increases with eachrepeated plasma processing cycle. However, for temperature profiles(A)-(G), each local temperature minima either increased at a slower rateor remained constant. FIG. 5 illustrates that lower thermally conductivemedium 250 and upper thermally conductive medium 260 are more effectiveat dissipating heat away from hot edge ring 238 and reducing first wafereffects. Testing at higher RF power (e.g., 3 kW and 4.5 kW) illustratessimilar trends.

Example 2

A series of tests were performed to determine the effectiveness ofpressurized helium in upper volume 366 (as upper thermally conductivemedium 360) in the FIG. 3B embodiment in dissipating heat from hot edgering 338 during plasma processing.

Tests were performed in an EXELAN® FLEX™ etching system, manufactured byLam Research Corporation, located in Fremont, Calif. For each test, four300 mm silicon wafers were subjected to plasma processing for 1 minute.A fifth 300 mm silicon wafer was then plasma processed for 6 minutes. Agas mixture of 25 SCCM O₂/35 SCCM C₄F₈/500 SCCM Ar was introduced intothe etch chamber at a pressure of 45 mTorr. Dual-frequency power wasapplied to a bottom electrode, in which the total RF power was variedfrom about 1 kW to about 4.5 kW; and total helium pressure was variedfrom about 0 Torr to about 30 Torr. The temperature of hot edge ring 338was measured with an fiber optic temperature probe during plasmaprocessing. Hot edge ring 338 and RF coupling ring 340 were mechanicallyclamped at a torque of about 4 in.-lb. and about 10 in.-lb,respectively. The material for lower thermally conductive medium 350 wasa Q-PAD® II gasket.

FIG. 6A illustrates temperature profiles of hot edge ring 338 as afunction of total RF power for: (A) about 0 Torr of helium staticpressure; and (B) about 30 Torr of helium static pressure. Thetemperature of hot edge ring 338 was measured after a fifth 300 mmsilicon wafer was processed for about 6 minutes. As illustrated in FIG.6A, pressurized helium at about 30 Torr can lower the temperature of thehot edge ring 338 up to 20° C. at a RF power of 4.5 kW.

FIG. 6B illustrates the temperature response of hot edge ring 338 asstatic helium pressure is varied from 0 Torr to 30 Torr in 5 Torrincrements. Initially, the static pressure of helium in upper volume 366was about 0 Torr during the application of 4.5 kW RF power. After thetemperature of hot edge ring 338 exceeded about 93° C., the staticpressure of the helium was increased to 5 Torr for about 1 minute,resulting in a temperature decrease of the hot edge ring to about 85° C.When the static pressure was increased to 10 Torr for about 1 minute,the temperature decreased to about 85° C. When the static pressure wasincreased to 15 Torr for about 1 minute, the temperature decreased toabout 79° C. When the static pressure was increased to 20 Torr for about1 minute, the temperature decreased to about 73° C. When the staticpressure was increased to 25 Torr for about 1 minute, the temperaturedecreased to about 72° C. When the static pressure was increased to 30Torr for about 1 minute, the temperature decreased to about 70° C.

FIG. 6B illustrates that the temperature of hot edge ring 338 can beadjusted on a 1 minute time scale. Furthermore, larger temperaturedecreases can be achieved at lower static pressures (e.g, 0 Torr, 5 Torror 10 Torr). Additionally, the FIG. 3B embodiment provides the abilityto adjust the temperature of hot edge ring up to about 20° C. to 25° C.at a total RF power of 4.5 kW by varying helium static pressure fromabout 0 Torr to about 30 Torr.

Example 3

A series of tests were performed to the effectiveness of pressurizedhelium in annular channel 364 as upper thermally conductive medium 360in the FIG. 3C embodiment in dissipating heat from hot edge ring 338during plasma processing. The experimental conditions for this series oftests were the same as described above for Example 2. The height ofannular channel 364 was about 2 mils.

FIG. 7A illustrates temperature profiles of hot edge ring 338 as afunction of total RF power for: (A) about 0 Torr of helium staticpressure; and (B) about 30 Torr of helium static pressure. Thetemperature of hot edge ring 338 was measured after a fifth 300 mmsilicon wafer was processed for about 6 minutes. FIG. 7A also includesthe temperature profiles from the FIG. 6A embodiment. As illustrated inFIG. 7A, annular channel 364 is effective to reduce the heat dissipatedfrom hot edge ring 338, thus increasing the temperature of hot edge ring338 in comparison to the FIG. 3B embodiment.

As illustrated in FIGS. 7A and 7B, the FIG. 3C embodiment provides theability to adjust the temperature of hot edge ring 338 up to about 25°C. to 30° C. at a total RF power of 4.5 kW by varying helium staticpressure from about 0 Torr to about 30 Torr. Additionally, thetemperature of hot edge ring 338 increases by about 20° C. to about 50°C. at a total RF power of about 4.5 kW, in comparison to the FIG. 3Bembodiment. For certain etching applications, if the temperature of hotedge ring 338 is below about 70° C. to about 90° C., undesirable polymerdeposits may form on hot edge ring 338.

Example 4

Tests were performed to illustrate the effectiveness of upper innerO-ring 363A and upper outer O-ring 363B in dissipating heat from hotedge ring 338 during plasma processing. A gas mixture of 25 SCCM O₂/35SCCM C₄F₈/500 SCCM Ar was introduced into the etch chamber at a pressureof 45 mTorr with a total RF power of 3 kW. The temperature of hot edgering 338 was measuring during the plasma processing of a 300 mm siliconwafer. The static pressure of the helium in volume 365 was maintained atabout 0 Torr. Inner O-ring 363A and outer O-ring 363B were composed ofVITON® fluoroelastomer.

FIG. 8 illustrates a temperature profile of the hot edge ring as afunction of time during plasma processing at a total RF power of 3 kW.From FIG. 7, two conditions were tested: (A) upper inner O-ring andupper outer O-ring at a static pressure of about 0 Torr; and (B) noO-rings at a static pressure of about 0 Torr. As seen in FIG. 8, theeffect of VITON® fluoroelastomer O-rings was to decrease the temperatureof the hot edge ring by about 25° C. after about 3 minutes of plasmaprocessing at a total RF power of 3 kW.

Example 5

A series of etching tests were performed to determine the effectivenessof lower thermally conductive medium 250 and upper thermally conductivemedium 260 in the FIG. 2A embodiment in achieving a uniform etching rateacross the diameter of a 300 mm silicon wafer.

Tests were performed in an EXELAN® FLEX™ etching system, manufactured byLam Research Corporation, located in Fremont, Calif. For each test, 300mm silicon wafers were blanket coated with a layer of organicphotoresist. A gas mixture of 25 SCCM O₂/35 SCCM C₄F₈/500 SCCM Ar wasintroduced into the etch chamber at a pressure of 45 mTorr.Dual-frequency power was applied to a bottom electrode, in which thetotal RF power was varied from about 1 kW to about 3 kW. Hot edge ring238 and RF coupling ring 240 were mechanically clamped at a torque ofabout 2 in.-lb. to about 5 in.-lb. Materials for lower thermallyconductive medium 250 and upper thermally conductive medium 260 includedSIL-PAD® gaskets, Q-PAD® 11 gaskets and KAPTON® gaskets. After theetching of the blanket photoresist layer was completed, etching rate(nm/minute) was measured across the diameter of the wafer.

FIGS. 9A-9C illustrate photoresist etching rate profiles as a functionof radial position for a total RF power of about 1 kW, about 2 kW andabout 3 kW, respectively. From FIGS. 9A-9C, five thermally conductivemedia were tested: (A) Q-PAD® lower and upper gaskets with a 2 in.-lb.torque; (B) Q-PAD® lower and upper gaskets with a 5 in.-lb. torque; (C)two SIL-PAD® lower gaskets; KAPTON® upper gasket with a 5 in.-lb.torque; (D) no lower thermally conductive medium; two SIL-PAD® uppergaskets; and (E) no lower or upper thermally conductive media.

As indicated in FIGS. 9A-9C (circled region indicted by arrow) thepresence of lower thermally conductive medium 250 and/or upper thermallyconductive medium 260 (curves A-D) influences etching rate of thephotoresist near the edge of the wafer (i.e., at a radial position near±150 mm). From FIGS. 9A-9C, it has been determined that Q-PAD® lower andupper gasket with a 2 in.-lb. torque and a 5 in.-lb. torque at a totalRF power of 2 kW and 3 kW produced the most uniform photoresist etchingrate.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

What is claimed is:
 1. A temperature-controlled hot edge ring assembly adapted to surround a semiconductor substrate supported in a plasma reaction chamber, the assembly comprising: a substrate support with an annular support surface surrounding a substrate support surface, a radio-frequency (RF) coupling ring overlying the annular support surface; a lower gasket between the annular support surface and the RF coupling ring, the lower gasket being thermally and electrically conductive; a hot edge ring overlying the RF coupling ring, wherein the substrate support is adapted to support a substrate such that an outer edge of the substrate overhangs the hot edge ring; and an upper thermally conductive medium between the hot edge ring and the RF coupling ring; wherein the thermally conductive medium comprises: an inner O-ring and an outer O-ring, the inner O-ring and the outer O-ring being concentrically arranged, wherein the inner O-ring, outer O-ring, the hot edge ring and the RF coupling ring define a volume, the volume adapted to contain pressurized heat transfer gas, wherein the heat transfer gas includes helium, neon, argon or nitrogen.
 2. The assembly of claim 1, wherein the inner O-ring and outer O-ring surround an annular channel formed in the RF coupling ring, the inner O-ring, the outer O-ring and the annular channel being concentrically arranged.
 3. The assembly of claim 1, further comprising: a controller; a temperature sensor adapted to measure a temperature of the hot edge ring during plasma processing and supply input signals to the controller; a heat transfer gas source and a vacuum pump connected to the volume, the gas source operable to increase a static gas pressure in the volume in response to the controller and the vacuum pump operable to evacuate the volume in response to the controller.
 4. The assembly of claim 1, wherein the substrate support is actively cooled with a chilled liquid.
 5. The assembly of claim 1, wherein the RF coupling ring is mechanically clamped to the annular support surface; and the hot edge ring is mechanically clamped to the RF coupling ring.
 6. The assembly of claim 5, wherein the RF coupling ring is bolted to the annular support surface; and further comprising a clamping ring having a radially extending flange and the hot edge ring having a peripheral recess configured to mate with the flange and secure the hot edge ring to the RF coupling ring, the clamping ring being bolted to the RF coupling ring.
 7. The assembly of claim 6, further comprising a polyimide ring between the clamping ring and the hot edge ring.
 8. The assembly of claim 7, wherein the RF coupling ring is composed of aluminum oxide, silicon, silicon carbide, or aluminum nitride; the hot edge ring is composed of silicon, silicon carbide or quartz; and the clamping ring is composed of a ceramic material.
 9. A method of controlling a temperature of the hot edge ring assembly of claim 3 during plasma processing of a substrate in a plasma processing chamber, the method comprising: supporting the substrate on the substrate support; introducing a process gas into the plasma processing chamber; energizing the process gas into the plasma state; measuring a temperature of the hot edge ring; decreasing a pressure of the heat transfer gas to the volume if the temperature of the hot edge ring is below a target temperature; or increasing the pressure of the heat transfer gas to the volume if the temperature of the hot edge ring is above a target temperature; and processing the substrate with the plasma.
 10. The method of claim 9, wherein processing the substrate with the plasma includes: (a) plasma etching a layer of semiconductor material, metal or dielectric material; or (b) deposition of conductive or dielectric material.
 11. A plasma processing apparatus comprising the assembly of claim 1, wherein the plasma reaction chamber is a plasma etcher adapted to etch semiconductor, metal or dielectric material; or a deposition chamber adapted to deposit conductive or dielectric material.
 12. A temperature-controlled hot edge ring assembly adapted to surround a semiconductor substrate supported in a plasma reaction chamber, the assembly comprising: a substrate support with an annular support surface surrounding a substrate support surface; a radio-frequency (RF) coupling ring on the annular support surface, wherein the RF coupling ring is mechanically clamped to the annular support surface; a thermally insulative medium between the annular support surface and the RF coupling ring; a hot edge ring overlying the RF coupling ring, wherein the hot edge ring is mechanically clamped to the RF coupling ring; and a thermally conductive medium between the hot edge ring and the RF coupling ring; wherein the thermally insulative medium comprises: a first inner O-ring and a first outer O-ring, the first inner O-ring and the first outer O-ring being concentrically arranged, wherein the first inner O-ring, first outer O-ring, the RF coupling ring and the annular support surface define a first volume, the first volume adapted to contain gas at a reduced pressure.
 13. The assembly of claim 12, wherein the thermally conductive medium comprises: a second inner O-ring and a second outer O-ring, the second inner O-ring and the second outer O-ring being concentrically arranged, wherein the second inner O-ring, second outer O-ring, the hot edge ring and the RF coupling ring define a second volume, the second volume adapted to contain pressurized heat transfer gas; or an upper gasket, the upper gasket being thermally and electrically conductive.
 14. The assembly of claim 13, further comprising: a controller; a temperature sensor adapted to measure a temperature of the hot edge ring during plasma processing and supply input signals to the controller; a heat transfer gas source and a vacuum pump connected to the first volume and second volume, the gas source operable to increase a static gas pressure in the first volume and the second volume in response to the controller and the vacuum pump operable to evacuate the first volume and the second volume in response to the controller; a heating element embedded in the RF coupling ring; and a power supply adapted to supply power to the heating element in response to the controller.
 15. A method of controlling a temperature of the hot edge ring assembly of claim 14 during plasma processing of a substrate in a plasma processing chamber, the method comprising: supporting the substrate on the substrate support; introducing a process gas into the plasma processing chamber; measuring a temperature of the hot edge ring; applying power to the heating element to increase the temperature of the hot edge ring if the temperature of the hot edge ring is below a target temperature; or terminating power to the heating element and increasing a pressure of a heat transfer gas in the first volume if the temperature of the hot edge ring is above the target temperature; energizing the process gas into the plasma state; and processing the substrate with the plasma.
 16. A temperature-controlled hot edge ring assembly adapted to surround a semiconductor substrate supported in a plasma reaction chamber, the assembly comprising: a substrate support with an annular support surface surrounding a substrate support surface, a radio-frequency (RF) coupling ring on the annular support surface; a lower thermally conductive medium between the annular support surface and the RF coupling ring, wherein the RF coupling ring is mechanically clamped to the annular support surface; a hot edge ring overlying the RF coupling ring, wherein the substrate support is adapted to support a substrate such that an outer edge of the substrate overhangs the hot edge ring; and an upper thermally conductive medium between the hot edge ring and the RF coupling ring, wherein the hot edge ring is mechanically clamped to the RF coupling ring; wherein at least one of the lower or upper thermally conductive medium comprises: an inner O-ring and an outer O-ring, the inner O-ring and the outer O-ring being concentrically arranged, wherein the inner O-ring, outer O-ring, at least one of: 1) the hot edge ring and the RF coupling ring; and 2) the annular support surface and the RF coupling ring define a volume, the volume adapted to contain pressurized heat transfer gas, wherein the heat transfer gas includes helium, neon, argon or nitrogen. 